otp_cheatsheet.adoc

OTP Cheatsheet

The details of OTP that you may have forgotten or never known!

Behaviors

gen_server	For implementing the server of a client-server relation
gen_statem	For implementing state machines
gen_event	For implementing event handling functionality
supervisor	For implementing a supervisor in a supervision tree

Applications

Application Types
Applications	Regular applications that define their own supervision tree
Libraries	A simple collection of modules and doesn’t implement an application behavior callback module

Start Types	Affect on Runtime when Application Terminates
temporary	Termination is reported but no other applications are terminated
transient	If application terminates abnormally all other applications and the runtime system are terminated
permanent	All other applications and the runtime system are terminated

Supervisors

Restart Intensity

The supervisor’s maximum restart intensity limits the number of restarts that can occur within an period of time. Restart intensity is specified as a map with two keys - intensity and period. Restarts are limited to the to number specified by intensity that occur within the number of seconds specified by period.

Child Specs

Child specs are maps with the following keys:

Key	Optional	Description
id	required	An identifier to use for the process
start	required	The MFA to use to start the process
restart	optional	See the restart types
shutdown	optional	brutal_kill or an integer timeout for workers. Must be infinity for supervisors.
type	optional	See the child types
modules	optional	The callback module if there is one

Child Types

worker	Any process that is not a supervisor
supervisor	A supervisor process

Restart Types

permanent	The process is always restarted
temporary	The process is never restarted
transient	The process is only restarted if it terminates abnormally

Restart Strategies

Strategy	Description
one_for_one	If one child process crashes only restart that process
one_for_all	If one child process crashes all other child processes are terminated and all of them are restarted
rest_for_one	If one child process crashes the rest of the child processes are terminated and the crashed process and other terminated processes are restarted
simple_one_for_one	Like the one_for_one strategy, but it can only dynamically start processes from a single child spec

OTP Design Principles Created by Stratus3D  Copyright 2018.  Source Code